A typical compressor for a cryogenic refrigerator has a helium supply line which delivers compressed helium to the cryogenic refrigerator, a helium return line which delivers helium from the cryogenic refrigerator to the compressor and, within the compressor, an internal bypass line which lies between the helium supply line and the helium return line.
Situated within the third line is a pressure relief valve, which may open a differential means of from 180 to 240 psi. The line containing the relief valve is present to prevent an excess of pressure from building up in the compressor or supply loop from unwanted flow in the refrigerator. When the maximum predetermined pre-set pressure is reached, the differential pressure relief valve will automatically open to bypass gas flow from the supply line to the return line. Relief valves usually contain a poppet valve which is closed by a spring mechanism, and is forced open when the working fluid pressure against the poppet valve exceeds the force of the spring mechanism, as is shown in U.S. Pat. No. 4,718,442 issued on Jan. 12, 1988 by Harry Nicoll. However, poppet valves used in cryogenic refrigerator compressors of the prior art have been subject to the problem of chatter. As the poppet valve opens and gas flows from the supply line to the return line, the gas pressure across the poppet valve will drop and the spring within the poppet valve will force the valve to close. As the poppet closes, the gas pressure increases again, which tends to open the poppet. These opposing tendencies will lead to resonant "chattering" when the natural period of oscillation of the poppet is equal to the frequency of the driving force created by the flowing gas. The magnitude of the noise from the chatter is many times greater than the background compressor noise and can be quite annoying to persons in the vicinity of the compressor. The chatter can also generate particles and small chips of metal debris which can inhibit sealing of the relief valve and contribute to increased wear due to chatter. The noise can be generated by a lateral or side to side motion of the poppet within the valve.